It is likely a good thing the Islanders are thinking about before and after the NHL’s three-day Christmas break as two separate things.

Because before it, when they were mired in the bottom of the league standings, the start of a third-period slide likely would have ended in a loss. After it, they managed to avoid that third-period collapse — barely — and held on for a 4-3 victory over the Capitals on Tuesday night at Barclays Center.

Despite giving up a goal to Andre Burakovsky with 6:55 to play in the third period to cut the Isles’ lead to 4-3, and then taking two penalties in the final 5:15, they still picked up their third win in a row, bridging the three-day holiday hiatus and creating new momentum.

“I think you can [carry momentum], but I don’t think it has, and that’s a big thing,” said Cal Clutterbuck, who opened the scoring with his third of the season 8:02 into the first. “It was nice for all of us to shut it down for three days and kind of spend a holiday like Christmas around friends and family.

“It kind of energizes the brain as much as it does the body.”

So now the Islanders (14-14-6) again try to find a way to keep relevance in the Eastern Conference playoff race. Despite their shortcomings, they have shown the ability to beat teams like the Capitals (20-9-4), against whom they have now taken two of three this season.

The Islanders celebrate a Cal Clutterbuck goal against the Capitals.AP

They did it with the return of Jaroslav Halak in nets, getting his first start since Dec. 13 — a 4-2 loss to the Capitals that preceded a four-game stretch when coach Jack Capuano and his staff decided to start Jean-Francois Berube and Thomas Greiss each for two games.

Greiss stopped 76 of the 79 shots he faced in collecting two consecutive wins going into the break, but he was not even dressed for this one as Halak got the nod and was solid in making 31 saves.

After the game, Capuano repeatedly went back to how well he thought Halak played. It was an honest assessment, but it coincided nicely with a not-so-subtle way to publicly push the value for Halak, the 31-year-old netminder who has been on the trade block for almost a month.

“If you get the goaltending that we’ve gotten, right off the bat you’re going to have a 75-percent chance to win the game,” Capuano said. “Our special teams have improved, our 5-on-5 play has improved, and it’s given us a little bit of confidence to beat some good teams.”

It also helped that the big offseason free-agent signing of Andrew Ladd has started to pay some dividends. Ladd scored twice to make it three goals in his past two games and seven in the first 34 games of his tenure as an Islander.

“I’ve been around long enough to know that when things start to go your way, you have to ride that as long as you can,” Ladd said. “Just keep putting pucks towards the net, and you need that to gain confidence and really elevate your game.”

Yet it was the hottest Islander of all, Anders Lee, who created his own breakaway and then buried a breakaway past Braden Holtby for what turned out to be the game-winner, 5:24 into the third, making it 4-2 and giving Lee his 12th goal in the past 16 games. It came just 43 seconds after Ladd scored his second of the game to make it 3-2, somewhat quieting the nerves that boiled up when Alex Ovechkin scored 1:17 into the final frame to tie it, 2-2.

But there still needed to be big stops by Halak as the Capitals pulled Holtby and had a 6-on-4 man-advantage in the waning moments. But those saves came, and with a New Year’s trip about to commence from Minnesota to Winnipeg, this second part of the Islanders’ schedule has begun on the right foot.

“We were able to get it going,” Ladd said, “so we’re going to ride this wave as long as we can.”